453
FXAK68 PAFC 190057
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 PM AKDT Tue Jun 18 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Thursday night)...

The upper level ridge that has been promoting the clear and
convective pattern over interior Southcentral is starting to edge
eastward as a front is pushing northward toward the southwest
Gulf. This pattern shift toward a more unstable airmass
approaching coastal Southcentral will push any remaining
convective potential northward in the Copper River Basin this
afternoon and evening. Areas of marine stratus that pushed up
Cook Inlet the last few mornings has dissipated, and is expected
to continue diminishing in presence the next few mornings as the
ridge moves eastward. Some patchy fog may form over the marine
zones, but this should dissipate rapidly as the day warms. Where
the stratus has not dissipated is over the Gulf and Prince
William Sound. The subsidence from the ridge and persistent
southwest flow onto the coast will make it difficult for this
stratus to clear out until Wednesday of even Thursday. Therefore
expecting from Seward to Valdez to Cordova to remain under this
marine stratus through tonight.

By Thursday, the pattern will have shifted enough to have cleared
out the low clouds, but with southeast flow aloft, more general
cloudiness is expected over Southcentral for the end of the week.
The stable stratus marine layer clouds over the northern Gulf of
Alaska to be replaced by stratiform clouds from the incoming
trough, all-in-all little change in sky coverage expected for
places like Kodiak. With the change in stability for Kodiak
however, light rain has begun, and is expected to continue for
Kodiak the next few days.

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS
(Days 1 through 3: This afternoon through Friday afternoon)...

Fairly benign weather persists through Friday afternoon as the
storm track remains south of Alaska. Several lows moving along the
periphery of the forecast area will keep periods of breezier and
wetter weather in the forecast, but no particularly hazardous
weather is expected at this time. Instead, the primary weather to
watch for Southwest Alaska will be the potential for thunderstorms
this afternoon, and on Thursday and Friday afternoons. For the
Bering Sea and Aleutian Islands, a ridge will bring the potential
for widespread low stratus and fog.

Forecast confidence is fairly good at the large scale, but there
are a few forecast details where uncertainty is greater. One
such detail will be the areal coverage and severity of fog across
the Bering Sea and Aleutian Islands. For now, have introduced a
large area of fog to the Western and Central Bering/Aleutians.
Fog is inherently difficult to forecast because it relies on
small-scale interactions that weather models have difficulty
representing. Further complicating this is the scarcity of weather
observations in the Bering Sea and along the Aleutian Chain,
making it difficult for us to monitor patches of fog moving
through the area. Subsidence under the ridge and plentiful
moisture from the Bering Sea will likely lead to areas of fog, but
the difficulty will be determining exactly where and exactly how
thick the fog may be.

The other forecast element with lower confidence is thunderstorm
potential. Currently, weather models are showing instability
across parts of Southwest Alaska for Thursday afternoon and Friday
afternoon. Thursday afternoon`s convection forecast will be
complicated by the potential for lingering cloud cover as a North
Pacific low will be located just south of the Alaska Peninsula.
Friday afternoon looks a bit better, but there are differences in
where the best thermal instability (and therefore, convective
initiation) will occur. Current thinking is that the Middle
Kuskokwim Delta and Western Alaska Range have the best chances of
seeing thunderstorms on both afternoons, with the potential for
Kuskokwim Delta to see thunderstorms Thursday afternoon if cloud
cover clears enough.

-KC

&&

.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)...

Mainland Alaska remains under the influence of an upper level
ridge extending from Northwestern Canada through the forecast
period. Warmer than normal temperatures are expected over the
Southern half of the Mainland. On the surface, thermal troughs
support widespread convection. Arctic areas continue under a broad
low, with the Northwestern Bering low looping back into Siberia
for Tuesday. A very broad low stretches from Kamchatka across the
Aleutians and Bering into the Gulf of Alaska and Eastern North
Pacific. Model guidance continues in good confidence through most
of the period, but outliers develop into the new week. A series of
troughs slip along the Aleutians, spreading showers over the
Alaska Peninsula Southwest Alaska and Kodiak Island through
Tuesday. In the far West, a better organized front moves into the
Central Aleutians and Bering through Tuesday. A trough from the
Eastern North Pacific low brings showers to coastal locations from
the Canadian Border to Prince William Sound for the weekend.

-Kutz

&&

.AVIATION...

PANC...Areas of stratus continue to linger around portions of the Cook
Inlet this afternoon with any MVFR ceilings in the northern
reaches of the inlet expected to become VFR by late afternoon.
VFR conditions are expected to continue from late this afternoon
through tomorrow.

-CC

&&


$$